A Study On Cover And Cut Top Down Tunneling Technology Of Long-Span Deep Underground Structure

The Shang-Xia Shuijing subway section of Shenzhen Metro Line 5 has several important and difficult points:(1) the section is 1091m long, the longgest section with cover and cut up down tunneling. Whether the tunneling method can be successful is unsure. (2) The ground water level is high and geology is poor, which makes the water-proof very diificult. (3) The pit is 26m deep and the span is 31m in maximum, to ensuring the structure stability during the construction is very important. (4) The section is located in urban area with very busy traffic, the construction could greatly affect the safety of the adjacent buildings and road traffic. Aiming at the above key points, this study obtianed following achievements:·Numerical modeling was carried out by using the finite differential method for various structural types, based on the existed exploration and design information. The modeling showed that (1) the design of the underground continuous walls, beams and plates can meet the stability requirement. (2) as it is shallow and the structure is compressed by the soil pressure, the structure tends to be up floating and floating-resistence beam is necessary. (3) Part of the strutures may not be stable only with underground continuous walls and plates and lateral steel support is suggested. (4) Some sections are cut in pillars which could affect the structure stability and lateral steel support is suggested.·By tracing the construction and analysing the difficulties met, a set of cover and cut up down tunneling technology in long subway sections has been proposed including the construction of underground continuous walls, structure joint skills, dewatering and drainage, and the construction technology of hole-drilling grouting piles.·This study developed a real-time monitoring and warning system for super long city subway sections at the first time in China. It summarised the difficulties encountered during the development and aspects needing further improvement in order to provide useful reference to future works.